Honesty and openness are the primary personality traits that long-term couples share

A recent study published in the Journal of Research in Personality suggests that long-term spouses share strong similarities in specific personality traits, particularly regarding honesty and openness. The findings provide evidence that while couples accurately judge each other’s personalities overall, they also tend to assume their partners are more similar to themselves than they actually are.

Psychologists often measure human personality using structured frameworks that group complex behaviors into broad categories. One prominent framework is the HEXACO model, which organizes human personality into six broad dimensions. These dimensions include Honesty-Humility, Emotionality, Extraversion, Agreeableness, Conscientiousness, and Openness to Experience. Each of these broad categories contains narrower sub-categories, known as facets, that describe specific behavioral tendencies.

For example, the Honesty-Humility dimension encompasses facets like fairness, sincerity, and modesty. The Openness to Experience dimension involves facets such as aesthetic appreciation, inquisitiveness, creativity, and unconventionality. Researchers use these detailed frameworks to understand how personality influences our daily choices, including the people we choose as long-term romantic partners.

In the context of romantic relationships, scientists often look at three distinct statistical concepts to understand personality dynamics. The first concept is self-partner agreement, which measures how accurately one person’s assessment of their partner matches the partner’s own self-assessment. A high score here means partners know each other very well.

The second concept is actual similarity, which looks at whether two partners genuinely share the same personality traits based on their individual self-reports. The third concept is assumed similarity, which describes a person’s tendency to perceive their partner as having the same personality traits as they do. Assumed similarity happens regardless of whether the couple actually shares those traits in reality.

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Past research looking into whether spouses have similar personalities has produced mixed results. Studies using another popular framework called the Big Five model often find very little actual similarity between spouses. This tends to suggest that people do not necessarily choose romantic partners with similar personalities, a finding that challenges the common idea that birds of a feather flock together.

However, studies using the HEXACO model have sometimes found different patterns, leading researchers to examine these dynamics in an older demographic. “Studies on whether social partners (friends and romantic partners) share similar personality traits show that partners are similar to each other in two personality traits, but only in those two traits — Honesty-Humility and Openness to Experience, and people often overestimate this similarity, a phenomenon known as assumed similarity,” said Kibeom Lee, a psychology professor at the University of Calgary and lead author of the study.

By focusing on older adults, the authors hoped to see how enduring marriages align with these earlier findings. “We wanted to find out whether this pattern is more prominent among long-term spouses than close friends or young romantic partners,” Lee said. “The data supported this expectation.”

To explore these personality dynamics, the researchers recruited participants through a certified Dutch internet survey panel. The final sample consisted of 451 heterosexual married or cohabiting couples from the Netherlands. This resulted in a total sample size of 902 individual participants.

The individuals in the study had an average age of about 55 years old, representing a mature demographic. The couples in this sample had a notably long history together. Their relationship lengths ranged from one year to just over 64 years. On average, the couples had been together for 28 years, providing an ideal testing ground for seeing how well partners know each other.

Each participant completed a standard personality questionnaire known as the HEXACO-100. This survey asks individuals to rate their agreement with various statements on a five-point scale, ranging from strongly disagree to strongly agree. The questionnaire reliably measures the six main personality factors as well as twenty-five specific facet traits.

The participants completed the questionnaire twice during the study. First, they filled it out to describe their own personal behavioral tendencies. Then, they completed the exact same survey again, but this time they answered the questions based on how they viewed their partner’s personality. This dual approach allowed the scientists to directly compare self-reports with partner-reports.

The data provides evidence of very high self-partner agreement across all measured traits. The statistical correlation for agreement averaged around 0.70, which is remarkably high in psychological research. This suggests that people in long-term relationships are extremely accurate at judging their partner’s true personality traits.

Openness to Experience showed the highest level of agreement among the six major traits. Spouses were particularly good at identifying their partner’s levels of inquisitiveness and appreciation for art and beauty. The researchers suspect that these high agreement scores might represent the practical upper limit of what a paper-and-pencil personality questionnaire can measure.

Interestingly, Honesty-Humility showed the lowest level of self-partner agreement among the major traits, though it was still relatively high overall. When the researchers looked closer at the specific facets of Honesty-Humility, they found that spouses had a harder time accurately judging sincerity and modesty. On the other hand, they were much better at agreeing on their partner’s levels of fairness and greed avoidance.

The authors suggest a few possible reasons for this lower agreement regarding sincerity and modesty. It is highly possible that individuals have a hard time objectively judging their own modesty, which skews their initial self-reports. It is also likely that internal traits like sincerity and modesty are simply harder for outside observers to judge accurately, even if the observer is a spouse of nearly three decades.

When looking at actual similarity, the study found a distinct pattern that separates the HEXACO traits from one another. Honesty-Humility and Openness to Experience were the only major traits that showed a strong positive similarity between spouses. If one partner scored high in honesty or openness, the other partner tended to score high in that specific area as well.

The other four major traits showed almost zero actual similarity. For instance, an extroverted person was just as likely to be married to an introverted person as they were to another extrovert. Only a few specific sub-traits of extraversion, such as social self-esteem and liveliness, showed a mild similarity between partners.

The findings for assumed similarity followed a similar pattern but were generally much stronger. Spouses naturally assumed they were highly similar in Honesty-Humility and Openness to Experience. In fact, for Honesty-Humility, the assumed similarity was significantly higher than the actual similarity calculated by the researchers.

This suggests that people tend to heavily project their own moral and ethical values onto their romantic partners. Because it is somewhat difficult to perfectly judge a partner’s internal sincerity or modesty, individuals might just assume their partner shares their own level of honesty. If a person values fairness and sincerity highly, they tend to believe their long-term partner holds those exact same moral values.

The authors urge caution when interpreting what these similarities mean for individual relationships. While sharing values is common, it is not a strict requirement for a successful marriage.

“The key takeaway is that social partners tend to be similar in Honesty-Humility and Openness to Experience because these traits are closely linked to people’s values and worldviews, which are important for starting and maintaining relationships,” Lee told PsyPost.

At the same time, differing personalities do not doom a romance to failure. The overall effect sizes observed in the data were notable but not absolute. “However, we should note that this similarity is only modest,” Lee added. “There are many happy and long-lasting couples who differ substantially in these traits.”

The researchers also note some limitations to their findings, along with directions for future study. The entire sample consisted of Dutch individuals, which represents a very specific Western cultural context. Dating and marriage practices vary widely around the globe, and these cultural differences might influence whether people choose partners with similar traits.

For instance, a previous study conducted in mainland China found almost zero similarity between romantic partners across all HEXACO traits, including honesty and openness. It is not fully understood if this discrepancy is due to differing cultural norms surrounding marriage in collectivist societies. It might also be due to differences in how people from various geographic regions interpret translated survey questions.

Future research should focus on testing these personality dynamics in other non-Western cultures to see if the patterns hold up globally. Scientists could also investigate exactly why specific traits like social self-esteem show slight similarities in couples. It is possible that sharing similar self-esteem levels helps maintain a romantic bond, or it could simply be that a couple’s shared life circumstances influence both partners’ self-esteem equally over time.

The study, “Self/spouse agreement, similarity, and assumed similarity in the HEXACO personality factors,” was authored by Kibeom Lee, Michael C. Ashton, and Reinout E. de Vries.